It looks like they're either a species of Acanthozoon or of Thysanozoon. The exact genus can only be determined by checking how many male pores there are on the ventral side. Both of these genera are characterized by papillate dorsal surfaces which are evident in these two picts.

It looks like they're either a species of Acanthozoon or of Thysanozoon. The exact genus can only be determined by checking how many male pores there are on the ventral side. Both of these genera are characterized by papillate dorsal surfaces which are evident in these two picts.